A great many different types of aftertreatment systems have been used in connection with internal combustion engines for decades. It is often desirable to remove particulates in exhaust from internal combustion engines, and exhaust particulate filters or “traps” are widely used for this purpose. While many exhaust particulate filters are quite effective at trapping soot, eventually the quantity of soot reaches a point at which continued operation of the engine becomes problematic or less efficient, or risks damaging the exhaust particulate filter. “Regeneration” is a term generally used to describe the process of cleansing an exhaust particulate filter of trapped soot. One common approach involves raising the temperature within the filter to a point sufficient to combust the trapped soot and convert it into less undesirable or more readily treated emissions.
A variety of different regeneration techniques are well known and widely used. Among these are the use of catalysts resident within an exhaust particulate filter or carried within engine fuel. Catalysts can assist in combustion of soot at relatively lower temperatures than what might otherwise be required. Other regeneration techniques utilize fuel injected into exhaust gases, which ignites upstream of or upon entering the exhaust particulate filter to increase the temperature therein. In-cylinder dosing of fuel or dosing into the exhaust downstream the engine are other techniques which raise filter temperature by way of an exothermic reaction without actually igniting the fuel. Electrically powered heaters, post-injections and back-pressure generating flow restriction mechanisms are also used to facilitate the combustion of trapped soot within an exhaust particulate filter. Known techniques generally have the disadvantage of expense, such as where fuel and/or catalysts are consumed, and often create efficiency penalties for the engine.
Detecting an amount of trapped soot within a filter with relative precision and accuracy can limit the frequency of regeneration, or enable regeneration at opportune times, such that the disadvantages associated with regeneration can be ameliorated. For this reason, engineers are continually seeking techniques to more accurately and precisely detect an amount of trapped soot so that underuse and overuse of regeneration can be avoided. Even seemingly miniscule improvements in detecting soot load, and thus conditions suitable for regeneration, can translate into significant real world gains in efficiency.
One general class of soot detection technologies employs electromagnetic energy transmitted through an exhaust particulate filter, and reduced in strength as a portion of the electromagnetic energy is absorbed by trapped soot. Such techniques have been known for a number of years, but rarely if ever achieve their full theoretical potential. Other soot detection strategies rely upon an observed pressure drop or phenomena related thereto, known generally as ΔP, of exhaust as it passes through an exhaust particulate filter. The relative flow resistance of the filter can be mapped to an amount of soot trapped therein. Known techniques tend to be computationally challenging, require the use of relatively expensive and complex hardware, or suffer from other shortcomings. Moreover, strategies which appear to perform acceptably in the lab or often discovered to be poorly suited to actual field conditions.